Fluorescent method of tracing movement of particles from a source to a test station using a solid solvent at the test station



United States Patent 3,231,738 FLUORESCENT METHOD OF TRACING MOVE- "MENT OF PARTICLES FROM A SOURCE TO A TEST STATION USING A SOLID SOLVENT AT .THE TEST STATION Frederick Fischer, 2631 Spruce St., Bakersfield, Calif. No Drawing. Filed June 17, 1963, Ser. No. 288,459

5 Claims. (Cl. 250--71) This invention relates to an improvement in meteorological tracing processes wherein a fluorescent tracer particle is used.

In many fields of science and technology it is desirable to be able to trace the dissemination of smoke, particulate matter, aerosols and thelike, which in general may be emitted from a localized source. Thus, for example, various man-made sources of air pollution, such as industrial smokes, operations involving explosives, both chemical and atomic, airborne sources such as rocket engine exhausts and the like, all call for knowledge of the extent to which the contamination arising therefrom is carried, dispersed, and perhaps eventually becomes fallout.

In one of the most satisfactory methods of tracing the nature of such airborne contamination, a soluble, fluorescent dye in particulate form is caused to be disseminated along with the source of contamination. Thus, it may be ejected along with the smoke from a smoke stack, or placed adjacent to an explosive charge, or the like, so that the fluorescent dye particles will accompany the contamination to be traced. By sampling the air at a number of stations distant from the source, the nature of the distribution of the contaminant may be learned.

A known technique of the general type described utilizes the water soluble fluorescent dye uranine, also known as sodium fluorescein, which is caused to be dispersed along with the contamination, or indeed, where purely meteorological information is desired, simply put into the air at a suitable location. The air is then sampled at selected test stations by aspiration through a paper filter, which is then washed with a small amount of water and the fluorescence if any detected by use of a fluorometer.

An object of the present invention is to provide an improved process for detecting the presence of air of soluble fluorescent dye particles.

Another object of the invention is to provide a process of using fluorescent dye particles which greatly increases the certainty that the particles found originate with the known source.

Other objects of the invention will appear as the description thereof proceeds.

Generally speaking and in accordance with illustrative embodiments of my invention, I cause to be disseminated into the atmosphere a multitude of finely divided particles of a fluorescent dye which is soluble in at least one solvent to give therein a fluorescing solution. I prefer, and

find best, to use the dye uranine, which is soluble in water to give a brilliant yellow-green fluorescent solution. In accordance with my invention, having dispersed the particles as aforesaid, I then set out at selected test stations a layer of a solidified solvent for the dye particle chosen. In the preferred embodiment, where uranine is used, I use water as the solvent and solidify it with a water dispersible gelling agent such as agar. I may also include in the solidified solvent a minor proportion of a relatively high boiling liquid compatible with the solvent, as an evaporation retardant. In my chosen system I include a fraction of 1% glycerin for this purpose. Again, to make it practicable to make up the solidified liquid considerably in advance of the actual test, I prefer to include a bactericide in the solidified solvent. One such material 3,231,738 Patented Jan. 25, 1966 compatible with the system just described and which I prefer, is benzalkonium chloride. A suitable formula is 96.5% water, 2% agar, 0.3% glycerine and 0.2% benzalkonium chloride. These ingredients are melted together, the solution filtered if necessary and then poured as a thin film onto suitable containers or substrata, such as Petri dishes, shallow aluminum foil dishes such as are used in bacteriological work or the like.

If the fluorescent dye selected is not soluble in water, but instead soluble in some organic liquid, then the solidified solvent must of course be chosen accordingly. Thus, for example, if anthracene is used (and throughout this disclosure and the claims which follow I use the term fluorescent dye in a broad sense to include organic substances exhibiting a fluorescence in solution, whether or not they find commercial use as a dyestuif in the ordinary sense), then a solvent in which anthracene is soluble and exhibits fluorescence must of course be chosen together with a suitable gelling agent or solidifying agent for the solvent. In the case of anthracene, hexane and carbon tetrachloride are suitable, and may be gelled with aluminum palmitate. It goes without saying that both the solvent and the gelling or solidifying agent selected must in themselves be non-fluorescent, for reasons which follow.

I have found that when proceeding in accordance with my invention when the liberated fluorescent dye particles fall onto the solidified solvent, they dissolve therein and diffuse outward as a ring or halo around the particle. This ring is made visible by observing the solidified sol vent when irradiated with light which causes the fluorescent dye to fluoresce. Thus, for example, when uranine is used, relatively long wave length ultraviolet is suitable. Uranine absorbs blue-violet light in the range 4400 to 5200 A., and emits a yellow-green fluorescent light in the range 5100 to 5900 A.

I may observe the ring of dissolved fluorescing dye in the solidified solvent by direct observation, as with a fluorescence microscope using either low, medium or high powered optics as required; or I may pick up the presence of the fluorescing dye particle in the solidified solvent film by any of various instrumental devices which are for the most part automated fiuorometers.

The great advantage of proceeding in accordance with my invention is that an actual count of individual particles is possible, and moreover the individual dye particles trapped on the solidified solvent surface are visible to observation. This is greatly in contrast to the system wherein a filter paper is simply washed with a solvent and put in a fluorometer, for in that case, one obtains only a single, overall reading, proportional to the total fluorescing material trapped. In my inventive process, the number, nature and distribution of the actual dye particles are revealed, and this is often of critical diagnostic importance, in tracing the nature and extent of the contamination.

Moreover, in accordance with a further elaboration of my invention, I include a mechanical mixture of two or even more different fluorescing dye particles. Thus, for example, I may mix uranine particles with rhodamine B extra particles. In observing the samplings on the solidified solvent, each uranine particle will show a yellowgreen fluorescent ring, while the rhodamine particle will exhibit a red fluorescent ring. This enables one to correlate a sampling with the particular tracer emissions with great certainty. While there is some possibility that some other investigator even hundreds of miles away may be using uranine as a tracer, by using a combination of two or more dyes exhibiting different fluorescence colors, the likelihood of an ambiguous result is reduced to a very low figure.

In general, my fluorescing dye particles as emitted into the atmosphere should be particle sizes within the range of about /2 micron to about 10 microns. Actually, a ground dye particle mass of around 1 to 2 microns is both practicable and highly suitable. In some cases, as for example where the output of a smoke stack is to be traced it is possible to make a water solution of the dye, such as uranine, and spray it through an atomizer of the ordinary type into the smoke stack. The droplets evaporate and leave a particle of dye within the desired range. Where two or more different dyes are used, in the variation of technique which has been described, then it is naturally essential to use a different solution for each dye and spray it through its own atomizer, so that particles will be produced which consist of but a single dye.

While I have described my invention with the aid of various specific examples, it will be clear that the invention is a broad one, and numerous variations of detail are permissible and indeed contemplated, within the scope of the claims which follow.

What I claim is:

1. The process of tracing atmospheric contamination from a source to a test station which comprises: emitting at said source a multiplicity of particles of a fiuorescing dye which is soluble in a solvent to give a fiuorescing solution; setting out a layer of said solidified solvent at said test station; irradiating said solidified solvent layer with light having a wave length which causes fluorescence in the dye-solvent system selected; and observing said itradiated layer to detect the presence of dye particles thereon.

2. The process of claim 1 wherein said dye is uranine.

3. The process of claim 1 in which said dye is uranine and said solvent is water.

4. The process of claim 1 in which said dye consists of discrete particles of at least two different dyes.

5. The process of claim 1 wherein said dye consists of discrete particles of uranine and of rhodamine B extra.

No references cited.

RALPH G. NILSON, Primary Examiner. 

1. THE PROCESS OF TRACING ATMOSPHERIC CONTAMINATION FROM A SOURCE TO A TEST STATION WHICH COMPRISES: EMITTING AT SAID SOURCE A MULTIPLICITY OF PARTICLES OF A FLUORESCING DYE WHICH IS SOLUBLE IN A SOLVENT TO GIVE A FLUORESCING SOLUTION; SETTING OUT A LAYER OF SAID SOLIDIFIED SOLVENT AT SAID TEST STATION; IRRADIATING SAID SOLIDIFIED SOLVENT LAYER WITH LIGHT HAVING A WAVE LENGTH WHICH CAUSES FLUORESCENCE IN THE DYE-SOLVENT SYSTEM SELECTED; AND OBSERVING SAID IRRADIATED LAYER TO DETECT THE PRESENCE OF DYE PARTICLES THEREON. 